1. Field of the Invention
The present invention relates to a device for controlling the depth of soil penetration of a ground contact implement (GCI). The invention permits presetting of a desired GCI soil penetration depth, and provides continuous dynamic regulating of an adjustable downpressure system in response to changing forces exerted on the device (e.g. including those forces resulting from soil unevenness) so as to maintain the GCI at approximately the preset desired depth. The present provides GCI position control, rather than simply utilizing hydraulic or pneumatic fluid pressure control, to regulate depth of GCI soil penetration.
2. Description of the Prior Art
Depth controls, for individual furrow opener units on planters and drills, including one or more wheels at either the front, sides or rear of an opener unit, were described by Morrison and Gerik, Trans. ASAE, Vol. 28, No. 5, p. 1415-1418, 1985. Depth control designs have also combined front and rear wheels on "walking beams" or in other linked arrangements to sense the average soil surface elevation and control the depth of planting in relation to that average elevation. The "linked-wheels" depth control concept reported by Morrision and Gerik (1985) citation supra is an example of this type design. While such prior art planter or drill opener unit depth control systems react to an interaction between vertical forces (e.g. weight of the furrow opener assembly, added ballast, variable down pressure of springs, the variable weight of seed or granular products in attached hoppers, etc.) and chosen depth controls, they suffer from the drawback of excess vertical forces (forces not required for furrow opening and closing) being supported by the depth control mechanisms and thereby causing wheel sinkage and row area soil compaction.
Also it is known in the prior art to utilize downpressure springs to transfer a portion of the main machine frame weight to the individual furrow opener units. However, if the downpressure of the spring is adjusted for adequate furrow opening in high resistance cutting condition, then undesirably high downpressure forces will be applied on portions of the field having lower cutting resistance, resulting in excessively deep planting.